Figure 1d shows the Fermi surface mapping of FeSe11111 measured at 20 K. The spectral weight at each momentum is obtained by integrating the EDC (energy distribution curve) spectral weight within [-10,+10] meV energy window with respect to the Fermi level (E\(_F\) ). The measured Fermi surface contains a nearly circular electron-like Fermi surface around M points (Fig. 1d). There is no indication of Fermi crossing around the \(\Gamma \)  (0,0) point. Such a Fermi surface topology is very similar to that found in the superconducting single-layer FeSe/SrTiO\(_3\)  film (Fig. 1e) with a superconducting temperature at \(\sim \) 55 K[1]}. In comparison, there are electron pockets around the Brillouin center in the A\(_x\) Fe\(_{2-y}\) Se\(_2\)  superconductor (Fig. 1f)[2]}, [3]}. The area of the electron pocket near M gives a good measure of the electron doping level for the strongly two-dimensional systems. Considering that the Fermi surface around M consists of two degenerate Fermi surface sheets, the estimated electron counting in FeSe11111 (Fig. 1d) is \(\sim \) 0.08 electrons/Fe. This is smaller than 0.10 electrons/Fe in single-layer FeSe film (Fig. 1e) with a T\(_c\)\(\sim \) 55 K[1]} and 0.12 electrons/Fe in vacuum-annealed single-layer FeSe/SrTiO\(_3\)  film with a T\(_c\)\(\sim \)  65 K[5]}. We note that the electron counting in both FeSe11111 and superconducting single-layer FeSe/SrTiO\(_3\)  film is much smaller than 0.18 electrons/Fe in A\(_x\) Fe\(_{2-y}\) Se\(_2\)  superconductor (Fig. 1f)[6]}, [2]}, [8]}, [3]} when only considering the M point electron Fermi surface sheet.
